240 children are in a school.
15 of the girls and
19 of the boys wear glasses.
40 children wear glasses.
- How many girls are there?
- How many boys are there?
- How many children do not wear glasses?
|
Number |
Girls |
Boys |
Total |
240 |
5 u |
9 p |
Wear glasses |
40 |
1 u |
1 p |
No glasses |
|
4 u |
8 p |
(a)
Number of girls = 5 u
Number of boys = 9 p
5 u + 9 p = 240 --- (1)
1 u + 1 p = 40 --- (2)
(2)
x 5 5 u + 5 p = 200 --- (3)
(1) - (3)
(5 u + 9 p) - (5 u + 5 p) = 240 - 200
5 u + 9 p - 5 u - 5 p = 40
4 p = 40
1 p = 40 ÷ 4 = 10
Substitute 1 p = 10 into (2).
1 u + 1 p = 40
1 u + 10 = 40
1 u = 40 - 10 = 30
Number of girls
= 5 u
= 5 x 30
= 150
(b)
Number of boys
= 9 p
= 9 x 10
= 90
(c)
Number of girls who do not wear glasses
= 5 u - 1 u
= 4 u
Number of boys who do not wear glasses
= 9 p - 1 p
= 8 p
Number of children who do not wear glasses
= 240 - 40
= 200
Answer(s): (a) 150; (b) 90; (c) 200